1. Field of the Invention
The present invention relates to a bump printing apparatus and a method of controlling the same, and more particularly, to a bump printing apparatus and a method of controlling the same that can increase the printability of solder bumps being printed on a board.
2. Description of the Related Art
In general, flip chip bonding, tape automated bonding and wire bonding are being used to interconnect external boards, such as printed circuit boards (PCBs) or wafer level packages (WLPs), to chips.
Among them, flip chip bonding has been widely used to manufacture portable electronic products, since this method increases the number of pads per unit area.
According to flip chip bonding, solder bumps are formed on a wafer in order to appropriately bond chips and external circuitry. Particularly, a technique for manufacturing solder bumps has been developed to form solder bumps having appropriate conductivity, uniform lengths and fine pitches.
According to this solder bump forming technique for flip chip bonding, the characteristics of solder bumps and an application range thereof are determined according to the materials used to form solder bumps. Examples of the solder bump forming technique may include a soldering method of contacting pad electrodes to solder, a screen printing method of forming solder bumps on pad electrodes by screen printing and reflowing the solder bumps, a solder ball reflow method of mounting solder balls onto pad electrodes and reflowing the mounted solder balls, and a plating method of performing solder plating on pad electrodes.
Among them, a screen printing method has been widely used to form solder bumps in that the process of forming solder bumps in this manner is simple, manufacturing costs are low, and bumps of desired metallic material can be formed.
Furthermore, a snap-off method of separating a mask and a board from each other after finishing screen printing includes a mask snap-off method in which a PCB is fixed and a mask is lifted to separate the mask and the PCB and a table snap-off method in which a mask is fixed and a table having a PCB mounted thereon is lowered to separate the mask and the PCB.
However, according to these methods, when the mask and the PCB are forcibly separated from each other, the mask sags and thus the speeds at which the mask and the board are separated vary according to portions. As a result, variations in the shapes of solder bumps and variations in the amounts of solder pastes being printed may occur.
Therefore, bump defects, such as the spreading of solder pastes, short circuits and missing bumps, in which bumps are not formed, occur to reduce the printability of bumps, which may reduce the reliability of printed circuit boards.